[libvirt] [PATCH] virprocess: Extend list of platforms for setns wrapper

[Martin Kletzander]

On Mon, Sep 15, 2014 at 05:36:16PM +0200, Michal Privoznik wrote:
>On 15.09.2014 17:32, Martin Kletzander wrote:
>> On Mon, Sep 15, 2014 at 04:22:18PM +0100, Daniel P. Berrange wrote:
>>> On Mon, Sep 15, 2014 at 05:20:46PM +0200, Michal Privoznik wrote:
>>>> On 15.09.2014 17:15, Martin Kletzander wrote:
>>>> >On Mon, Sep 15, 2014 at 03:43:55PM +0200, Michal Privoznik wrote:
>>>> >>Currently, the setns() wrapper is supported only for x86_64 and i686
>>>> >>which leaves us failing to build on other platforms like arm, aarch64
>>>> >>and so on. This means, that the wrapper needs to be extended to those
>>>> >>platforms and make to fail on runtime not compile time.
>>>> >>
>>>> >>The syscall numbers for other platforms was fetched using this
>>>> >>command:
>>>> >>
>>>> >>kernel.git $ git grep "define.*__NR_setns" | grep -e arm -e powerpc -e
>>>> >>s390
>>>> >>arch/arm/include/uapi/asm/unistd.h:#define
>>>> >>__NR_setns                   (__NR_SYSCALL_BASE+375)
>>>> >>arch/arm64/include/asm/unistd32.h:#define __NR_setns 375
>>>> >>arch/powerpc/include/uapi/asm/unistd.h:#define
>>>> >>__NR_setns               350
>>>> >>arch/s390/include/uapi/asm/unistd.h:#define __NR_setns          339
>>>> >>
>>>> >>Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>>>> >>---
>>>> >>src/util/virprocess.c | 18 ++++++++++++------
>>>> >>1 file changed, 12 insertions(+), 6 deletions(-)
>>>> >>
>>>> >
>>>> >NACK, we shouldn't be duplicating syscall definitions.  There should
>>>> >be AC_CHECK_FUNCS([setns]) (instead of AC_CHECK_FUNCS_ONCE() for the
>>>> >syscall) and having with_lxc = "yes" and ac_cv_func_setns != "yes"
>>>> >should result in an error.
>>>>
>>>> The only problem with this might be that on systems with older glibc
>>>> (and
>>>> there is plenty of them) libvirt will fail to build / miss this
>>>> feature. And
>>>> it's not that the kernel doesn't support the namesapces. But let me
>>>> see if I
>>>> can get some ACKs on that approach you're suggesting.
>>>
>>> That's basically what the code did before we added the #define or
>>> NR_setns.
>>> We took the patch specifically to help Debian where the kernel has it but
>>> glibc is outdated.
>>>
>>
>> Either Debian should patch their glibc or we should at lease use
>> SYS_setns IMHO.
>
>That's not gonna fly either. On my system, the SYS_setns is declared in:
>
># grep -r SYS_setns /usr/include/
>/usr/include/bits/syscall.h:#define SYS_setns __NR_setns
>
>And the syscall.h belongs to glibc, not kernel headers. So we are back
>at the start.
>

Well, I'd argue that we're not :)  Distros could make our lives easier
by not requiring us to guess their kernel's syscall numbers :)

>Michal
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